The present invention relates to a step-down power supply; and, more particularly, to a step-down power circuit capable of extending operating time of a battery-operated power supply, a method for driving same, and further an electronic module implementing same.
Conventionally, the voltage of a battery is lowered to a regulated level by a step-down switching made power supply in order to drive electronic circuitry of a portable electronic equipment, e.g., a notebook personal computer or a mobile phone.
Referring to FIG. 1, there is illustrated a conventional step-down switching power supply including an inductor 12 (an inductor for performing a smoothing operation, referred to as an inductor hereinafter), a first switching device 13, a smoothing capacitor 14, a rectifying diode 15, a second switching device 16, a smoothing capacitor 17 and a control IC (integrated circuit), i.e., a controller 18.
The first switching device 13 is, e.g., an P-channel field effect transistor (FET) and serves to convert an input voltage (Vin) provided from a battery (not shown) through an input terminal lla to an output voltage (Vout) provided to an output terminal 11b via the inductor 12.
The smoothing capacitor 14 is connected between the output terminal 11b and the ground. The rectifying diode 15 is connected in parallel with the series connection of the inductor 12 and the smoothing capacitor 14 to sustain an electric current of the inductor 12. The second switching device 16 is also an, e.g., N-channel FET and is coupled to the rectifying diode 15 in parallel. The smoothing capacitor 17 is coupled between the input terminal 11a and the ground.
The controller 18 detects the output voltage (Vout) on the output terminal 11b and controls an on-off operation of the first and the second switching device 13 and 16 such that the output voltage (Vout) can be maintained at a predetermined level. The switching devices 13 and 16 are controlled in such a manner that when the first switching device 13 is on, the second switching device 16 is controlled to be turned off, and vice versa.
According to the above described power circuit, when the switching device 13 is on, the input voltage (Vin) from the input terminal lla is smoothed by the inductor 12 and the smoothing capacitor 14 and outputted to the output terminal 11b. Meanwhile, the controller 18 adjusts pulse widths of pulse signals, which control the on-off conversions of the first and the second switching device 13 and 16, depending on a variation of the output voltage at the output terminal 11b to perform a feedback control. Accordingly, the regulated constant output voltage can be generated on the output terminal 11b.
As can be seen in FIG. 2, the controller 18 sets up a certain amount of dead time (tDET) between an on-state of the first switching device 13 and that of the second switching device 16. Such dead time is required to prevent an undesirable cross current which can occur when both of the switching devices 13 and 16 are turned on concurrently.
Due to such complementary on-off operation of the first and the second switching device 13 and 16, the energy accumulated in the inductor 12 can be emitted during a time period when the switching device 13 is off through the second switching device 16, even when connected to the output terminal 11b is a heavy load (not shown) requiring a great amount of electric current. Accordingly, a highly efficient synchronous rectification can be achieved without suffering from a forward voltage loss which can be otherwise caused by the rectifying diode 15.
In the step-down switching power circuit described above, the respective switching devices 13 and 16 are respectively set to be on and off simultaneously when the input voltage from the battery is reduced down close to the output voltage; and the switching device 13 is maintained at a conduction state without performing any further switching operations in order to maintain the output voltage at the regulated level and extend the operating time of the battery operated power circuit.
However, a considerable voltage drop occurs due to an electric resistance of the switching device 13 and the inductor 12 coupled in series between the input terminal 11a and the output terminal 11b. As a result, the output voltage Vout cannot be maintained at the regulated value even though the switching device 13 is controlled to be on without interruption.
As shown in FIG. 3, the input voltage Vin from the battery gradually decreases as the operation time of an electronic equipment increases. The output voltage Vout declines slowly after the input voltage Vin reaches a certain voltage value V1 at a time t1. The voltage V1 is the sum of a preset output voltage Vset and a voltage-drop Vdrp, i.e., V1=Vset+Vdrp, wherein the voltage-drop Vdrp is produced by a series resistance Ri1 of a turn-on resistance R1 of the switching device 13 and a resistance RL of the inductor 12.
Beyond t1, the output voltage Vout continuously decreases to reach Vmin at a time t1xe2x80x2 the input voltage Vin decreases. The portable electronic equipment ceases its operation when Vout drops down to Vmin, the minimum operation voltage of the electronic equipment. As a result, the operation time of the electronic device can be extended by t1xe2x80x2xe2x88x92t1, which is limited by the considerably large constant voltage drop Vdrp.
It is, therefore, an object of the present invention to provide a battery-operated step-down power circuit having longer operating time with wide range of operating condition, a method for driving such power circuit, and an electronic component or module capable of implementing the power circuit.
In accordance with a preferred embodiment of the present invention there is provided a power circuit capable of converting an input voltage into an output voltage through a switching and a smoothing operation, comprising: a switching device for performing the switching operation; an inductor for performing the smoothing operation, wherein the inductor is connected in series to the switching device; and a current control device connected in parallel to the switching device and/or the inductor.
In accordance with another preferred embodiment of the present invention, there is provided a power circuit, having a switching device and an inductor connected in series between an input terminal and an output terminal, for generating an output voltage on the output terminal by lowering an input voltage provided through the input terminal by a switching operation of the switching device and monitoring the output voltage to maintain the output voltage at a substantially constant level, the power circuit comprising: a current control device for adjusting an amount of an electric current provided from the input terminal to the output terminal in response to a control signal, wherein the current control device is connected between the input terminal and the output terminal in parallel to the switching device and an inductor; and a driving means for generating the control signal for controlling the current control device to maintain the output voltage at the constant level.
In accordance with still another preferred embodiment of the present invention, there is provided a driving method of a power circuit having a switching device and an inductor connected in series between an input terminal and an output terminal, wherein the power circuit generates an output voltage on the output terminal by lowering an input voltage provided through the input terminal by a switching operation of the switching device and monitors the output voltage to maintain the output voltage at a substantially constant level, the driving method comprising the steps of: providing a current control device for adjusting an amount of an electric current provided from the input terminal to the output terminal in response to a control signal, wherein the current control device is connected between the input terminal and the output terminal in parallel to the switching device and an inductor; and controlling a driving means for generating the control signal for controlling the current control device to maintain the output voltage at the constant level.
In accordance with still another preferred embodiment of the present invention, there is provided an electronic component for use in a power circuit, comprising: a package; an input terminal provided on the package; a first output terminal provided on the package; and a second output terminal provided on the package, wherein the package includes a switching device installed within the package and connected between the input terminal and the first output terminal; a current control device for changing an amount of an electric current provided from the input terminal to the second output terminal based on a control signal, wherein the current control device is installed within the package and connected between the input terminal and the second output terminal; a first control terminal connected to a control terminal of the switching device and installed to be exposed from the package; and a driving circuit for operating the current control device after the switching device is set to sustain an on duty factor of 100%, wherein the driving circuit is installed within the package and connected to a control terminal of the current control device.